Hello everyone, really need some input to help make an intelligent choice here. I'm building my 87 Iroc again, new engine, trans, and rear. I'm running a very well built 700R4 and a 10 bolt with eaton true trac with 3.73 gears and new axles.

For the motor..... I have a older 68-73 350 crate motor with a very minor build. I also have the factory 350 roller that was stock in my car, which 5 years ago (6000 miles) I had line bored and the deck machined. I reused all the factory lower end which now has a total of 127K on it. It also has a comp cam, duration @ .050 - 230 236 with lobe sep 113 degrees. The factory heads had a huge port/polish job done by a local machinist, unfortunately I don't have any flow numbers.

I'm would like to make over 400 at the crank, but be streetable. I'm running a carb because I was fed up trying to run the HSR that I had. I could never tune it, I think because I had too big of a cam on a factory lower end, maybe? What motor should I build? Any help is greatly appreciated. Thanks

 

kind of going through the same issue as you. wondering the same thing

 

Use the 1 pce block because it has provision for the roller cam

 

The more truer question here is a roller engine vs a flat tappet engine.And the roller having more machine work done to it.These days a new engine or say a crate engine can and does mean many things.Honestly some crate engine's are real junk.

That said,atleast with deductive logic,you know what was done machine work wise with the roller and having the added bonus of the roller cam and all those features you know come along with them.A stock bottom end should not effect the tune of a EFI system or should not have a problem handling 400hp at the flywheel.While I am at the flywheel,two pc flexplates do not interchange with one pc flexplates.I know that because my 383 build is a two pc crank using a adapter to a roller block for a one pc rear and I have to buy a two pc flexplate.The amount of miles on that roller makes it still a baby with many miles left in it.If you wanted to go through it and freshen it up with new rings and bearings,I would think it would be a fresh hone and go easy walk in the park.It being a roller,it's just a better deal overall.

When you say it was decked,it matters what the end SCR was given what the head camber volume is and given the cam choice was made based on the SCR.You can over cam a too low of a compression ratio and that will create havoc in the tune of a EFI.A 113 lope separation is kind of a odd ball number because most are 110,112,114 etc.A 112 number or above is right in the ballpark for a easier tune.The wrong cam choice can and does effect the DCR and there again that choice is all dependent on compression ratio's.So on a need to know basis you do need to know if the block was decked to 0 or .010 down and there again those are common numbers.Also which pistons where used to know what cc those are.If those stock heads are 76cc heads ported or not,0 decked or .010 down,they are hurting you.A stock head ported,you "might" be lucky to get a 170cc intake runner.And even if I am telling you compression ratios matter,a large portion of the power made is in the intake,heads,cam and kit.The summary is in the overheads.Yeah guys before someone jumps on me about headers and ignition.I matters to start at where the air comes in first because it is illogical to have good headers scavenge a engine that isn't well matched up so it doesn't breath right.

EFI vs carb??.Well you said you went back to a carb because of a problem tuning.Truth be know EFI's have a much better fuel management once tuned correctly and matched up with the right parts.Here is a article on EFI's for maybe some tips or just the entertainment value.

http://www.popularhotrodding.com/tec...guy/index.html

A properly tuned TBI should be able to obtain 400 at the flywheel.

 

I dont know properly tuned TBI's should be capable of a lot but I've never known anyone to get any kind of decent numbers out of them. The fastest GM based TBI I've ever seen is still a mid 14 second car with 13 second parts. 400 fwhp is good for 12's in these cars.

And building a new Gen I sbc is bad enough, doing it with a flat tappet block is a huge mistake. Go modern OE roller block all the way and dont look back.

400 fwhp with a 350 will need aftermarket aluminum head that AREN'T PROCOMPS. You may be able to get REALLY close with a Vortec heads 350 and a moderate hydraulic roller cam, like an XR276. Those seem to hit the 350-380fwhp range with Vortec heads. But 400 fwhp is a lot to ask from a 350. You might need to spin it to 6500 RPMs, at least 6000 even with top of the line aluminum heads. You're knocking on the limits of the envelope for Vortecs, and those are the only factory heads in the ball park for what you're trying to do.

Now if you take that roller block and build a 383 you can go larger on the cam, but you wont make much more power with Vortecs than you would with the 350, but it will be a lot more streetable. You could probably hit 400 fwhp with a Vortec heads 383 but you will need to be VERY careful to keep your compression ratio reasonable... that means a piston dish in the 15cc range.

And to be clear, Im not suggesting you go Vortecs... you'll make a lot more power a lot easier with some aftermarket aluminum heads. But the point Im trying to make is ANY factory head will come up short, the only ones that will get close are Vortecs.

 

Yeah-375 to 400 is the top end of a TBI.

 

Thanks for your replies, I really appreciate it. I'm thinking of using the newer block, although I really have no way to find out what the deck height is. Some more research and I'm sure I can measure it some way. Currently thinking of building a 383 with a trick flow upper kit that includes the heads, intake, and cam. That should get me where I need to be. Any further info is always welcomed, but thanks again for the help.

 

The corollary measurement to deck height, which I feel is kind of more important, is how far down the hole the slug is. That's what matters when calculating compression ratio. Also, a 1 pc. seal is a lot more resistant to leaks.

 

Factory deck height is 9.025 inches. Not that it matters since, as mentioned, how far in the hole the pistons are is far more important and these are VERY specific numbers and tolerances just arent tight enough to make assumptions about what exactly something should be. When assembled you will have big variances from cyinder to cylinder with those measurements. Just stack the deck in your favor for a good average.

Take the newer block to a machine shop - they can measure the deck height if it matters to you. It should, but mostly just because it's better to have the pistons as close to the deck as possible. Pay close attention to pin or "compression height" numbers on pistons when you're looking at them.

You'd be silly to use the old block when you have a new roller block you can use. I'd even be tempted to use a roller 305 over a flat tappet 350 for a few different reasons. You will NOT hit 400 fwhp with a flat tappet 350 unless you build a really, REALLY outlandish setup that will be a horrible pain to live with for street driving.